This study involves the characterizations of two proteins from brain. The proteins are neuron specific enolase (NSE) and non-neuronal enolase (NNE). Both proteins are isoenzymes of the glycolytic enzyme enolase in brain. NSE is localized in neurons and NNE in glia. The functional characterization and comparison is expected to provide information relating to the nature and regulation of brain energy metabolism at the neuronal and glial level. Both proteins have been purified; they are distinct kinetically and probably functionally. The neuronal enzyme is stable in the presence of salts such as KCl and NaCl, whereas the glial enzyme is inactivated. Studies of NSE levels in various neuroblastoma cells have indicated that this protein is a molecular correlate of differentiation and that its levels are responsive to dibutryl cAMP treatment. BIBLIOGRAPHIC REFERENCES: Marangos, P.J. and Zomzely-Neurath, C.: Determination and Characterization of Neuron Specific Protein (NSP) Associated Enolase Activity. Biochem. Biophys. Res. Commun. 68:1309, 1976. Marangos, P.J., Zomzely-Neurath, C. and Goodwin, F.K.: Structural and Immunological Properties of Neuron Specific Protein (NSP) from Rat, Cat and Human Brain: Comparison to Bovine 14-3-2. J. Neurochem. 28:1097, 1977.